In a fluid rotary machine, e.g., pneumatic pump, liquid pump, a reciprocating drive mechanism, in which a piston assembly connected to a crank shaft is reciprocated to repeatedly suck and discharge a fluid, is mainly employed; further, a rotary type compact fluid rotary machine, which has a long stroke, in which double-head pistons are disposed in a crisscross arrangement and in which the double-head pistons connected to a crank shaft are linearly reciprocated, on the basis of the principle of hypocycloid, by rotating a shaft so as to repeatedly suck and discharge the fluid, is also provided (see Patent Document 1).